It was very common practice in antiquity for the author of a book or letter to use a scribe/amanuensis (see descriptions in letters of Cicero, for example), and the use of a scribe is attested or implied by some New Testament documents, e.g. Tertius in Romans, possibly Silas in 1 Peter, the “we” in John 21:24:
This is the disciple who testifies to these things and who wrote them down. We know that his testimony is true.
I have no difficulty believing a well-traveled 1st century Galilean spoke Greek (see here), but I suspect the services of a scribe would be of great benefit in setting a full Gospel down in writing.
I am intrigued by a passage from the “Anti-Marcionite” prologue to John:
“The Gospel of John was revealed and given to the churches by John while still in the body, just as Papias of Hieropolis, the close disciple of John, related in the exoterics, that is, in the last five books. Indeed he wrote down the gospel, while John was dictating carefully” (translation by De Bruyne)
The prologue has been variously dated from the 2nd to the 4th century. Papias lived in Hieropolis; Irenaeus tells us John resided in Ephesus (a few days' journey away) until the times of Trajan (see vs 4 here), well within the adult lifetime of Papias.
Unfortunately, Eusebius says nothing about this. Given Eusebius’ general dislike for Papias, and his efforts (contra-Irenaeus in chapter 39 here) to downplay Papias’ possible association with John, this is not all that surprising.
Although Papias’ writings are lost and we can’t directly fact check the prologue, what intrigues me is that whoever wrote the prologue knew that their readers could fact check it. And the prologue was still considered credible enough that it shows up in 10 different surviving manuscripts.
How credible is this statement? Is it likely that Papias was the amanuensis for the Gospel of John?